On the hottest plastic packaging materials

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Plastic packaging materials complete the tensile, peeling, tearing, tightening and other mechanical properties of samples (Part 1)

plastics are widely used in the packaging industry without affecting the function of materials because of their unparalleled excellent properties. More than a quarter of modern plastic production is used to make packaging materials. The plastics commonly used in packaging mainly include polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyurethane and phenolic resin

1. Polyethylene (PE)

polyethylene is a high molecular polymer of ethylene and a thermoplastic. According to its industrial production methods, there are high-pressure, medium pressure and low-pressure polymerization methods. The molecular structure varies greatly with different production methods, and the product performance also varies with the molecular structure

polyethylene is a milky white waxy solid, which is lighter than water, softer, good water resistance, low temperature resistance, tasteless, non-toxic, poor heat resistance, poor air tightness of the film, and sensitive to ultraviolet light. It is easy to oxidize and age, with large changes in thermal shrinkage and poor printing performance. According to its density. It can be divided into high-density, medium density, low-density polyethylene, and linear low-density polyethylene

2. Polypropylene (PP)

polypropylene is a by-product of petroleum refining, propylene, refined propylene monomer, polymerized under the catalysis of catalyst, and then separated from the polymer. The molecular weight is 100000 ~ 500000, and the density is very small, which is the smallest of known plastics; Non toxic, tasteless, high transparency, good mechanical properties, surface strength, friction resistance, chemical corrosion resistance and moisture resistance; When the temperature is above room temperature, the impact resistance value is large, but the low temperature impact resistance value is small; It is easy to carry static electricity and has poor printing performance

polypropylene has a wide range of raw materials, low price and wide performance adaptability. It is widely used in the food industry. It is mainly used to make films and composite films. It has good transparency and surface gloss, and can withstand 120 ° C temperature; It can be made into packing boxes, blow molded into plastic bottles, and some machine parts can be made by adding some fillers

3. Polystyrene (PS)

polystyrene is the alkylation reaction of ethylene and benzene under the catalysis of anhydrous alumina to produce ethyl benzene, and then through catalytic dehydrogenation to obtain styrene. Styrene monomer is heated and polymerized in an aqueous suspension of an appropriate amount of initiator (benzoyl peroxide) and dispersant (polyvinyl alcohol) to form polystyrene. Polystyrene is a colorless, transparent, non ductile thermoplastic; It is non-toxic, tasteless, odorless, with good coloring, higher moisture permeability than polyethylene, low moisture absorption, stable size, and good gloss; Good processing performance and low cost; The mechanical properties increase with the increase of molecular weight; Low heat resistance, can not be used in boiling water; Low temperature resistance, able to withstand - 40 ℃ low temperature; Good indoor aging resistance; The causes and troubleshooting methods of such faults caused by alcohol organic solvents and minerals: (1) the hardness tester has good resistance to the uneven oil installed, and the acid and alkali resistance can also greatly improve the measurement range and accuracy of the sensor; OK

polystyrene is widely used because of its superior performance, low price, and can be made into films and containers, which are widely used in the food industry; The shrinkage rate can reach 60 ~ 70%. It is a good material for making shrink packaging. It has good insulation performance and can make a variety of telecommunication parts; It can also make various machine parts, toys, daily necessities, etc; Adding foaming agent into polystyrene can produce foamed plastic, which is a good cushioning packaging material

4. Polyvinyl chloride (PVC)

polyoxyethylene is polyvinyl chloride produced by suspension polymerization or lotion polymerization of vinyl chloride through the action of additives. It is light brown, transparent, and has good toughness, with a density of 1.4g/cm. It has good chemical stability and is not easy to be corroded by acids and alkalis; Good air tightness, water resistance, heat sealing performance, good printability, low production energy consumption and low price; Mechanical strength, wear resistance and pressure resistance are better than polyethylene and polypropylene. The main disadvantages are poor thermal stability, easy to decompose when heated, and release hydrogen chloride gas. Due to the different varieties and quantities of additives, such as plasticizers and stabilizers, PVC can be made into different products and hard products, such as hard pipes, building materials, etc; It can make artificial leather, wire and cable insulation, plastic floor, etc. Its main function in packaging is to make film, which is divided into soft film, hard film and shrink film. The soft membrane has soft texture and good heat sealing property, which is suitable for high-frequency sealing; Low tensile strength and high tear strength; Poor slip and processing performance. The tensile strength and tear strength of the hard film are large, the texture is hard, and the elongation is small; Low moisture permeability, good gas resistance and good sliding property; Printing adaptability is good, but appropriate ink solvent should be selected; Poor temperature resistance, brittle at low temperature. The shrink film has good transparency, low permeability, shrinkage when heated, wide shrinkage temperature range and large shrinkage rate. It is a good heat shrinkable packaging material. According to different production processes, it can be divided into dry stretching. Tubular stretching and longitudinal and transverse unidirectional stretching

5. Polyester (PET)

polyester is the condensation product of terephthalic acid and ethylene glycol. Compared with other plastics, polyester has excellent barrier properties, such as carbon dioxide, oxygen, water and fragrance; With excellent mechanical properties, it has high strength, compression resistance and impact resistance; Good chemical stability, acid and alkali corrosion resistance; High transparency, good gloss and optical properties; Non toxic, tasteless, in line with food hygiene standards; Its structure has ester group, so it has good printing performance. Polyester is a unique and widely used packaging material, which can be used to make films, bottles, cans, cups and other packaging containers, as well as dual-purpose baking trays

6. Phenolic plastic (PF)

phenolic resin is formed by condensation of phenols (mainly phenol) and aldehydes (mainly formaldehyde). According to the acidic or alkaline catalyst and the different ratio of phenol to formaldehyde, thermoplastic resin or thermosetting resin can be obtained. The two can be transformed into each other under appropriate conditions. Thermosetting resin is often used in practice. Phenolic resin has good mechanical strength and thermal strength; Good moisture resistance and corrosion resistance; Easy to process and low price. (to be continued)

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